At times we see dreams that mark time or past events, and many times this occurs on, or about the anniversary date of that event. From your comments I see that this dream is one of those, but there is more that is being addressed.
Your approach to the house, in which he once lived, represents a visit, (on your part), to the thoughts and feelings that you have repressed, or perhaps do not often allow yourself to live out, regarding your grand-dad. It has been a year since his passing and just now you are feeling up to a visitation. This supports your feelings of guilt, as shown in the dream, and reveals your innermost feelings thereof. Your unconscious mind has constructed a dream in which you could experience your feelings of love for this special person in your life, and simultaneously resolve any feelings of guilt that you harbor for not being able to face the emotions. "healing through dreams" what an incredible gift!
Our unconscious mind is our mentor and friend, and so much more!
A bit more... Going forward, you should not hesitate to tap into the the wisdom and love that your grandfather has shown you while he was alive. The unconscious mind meticulously stores and files every innuendo of his existence and it is there for you. In a manner of speaking, he is alive within you and there to console you or advise when things get rough...
all the best,
sailrmc